The present invention relates to vehicles adapted to ride over snow and commonly called "snow cats." Such vehicles are often used to groom ski slopes and also can be used as construction or transportation vehicles in snow-covered areas.
Snow cats found in the art generally employ a substantially rigid frame having track assemblies mounted at each corner or single track assemblies on each side. The rigid frame prevents the snow cat from conforming to mounds and other irregular features in the terrain. When a track assembly encounters an obstruction, the entire vehicle must traverse it. As a result, often only a small portion of the track assemblies of the vehicle may be in contact with the snow in a rugged area and some of the tracks may be lifted out of the snow decreasing the vehicle's purchase of the snow.
In order to turn snow cats found in the art, the speed of the tracks on one side of the frame is reduced or stopped without changing the speed on the other side. Since the track assemblies found on these snow cats are relatively narrow, this in an effective albeit inefficient method for turning the vehicle. Even with narrow track assemblies turning in this manner digs up a large volume of loose snow. This is undesirable on a ski slope, and such turning must either be done gradually or off to the side of the slope. With relatively wide tracks the vehicle cannot rotate efficiently since the elongate grousers on such a track will dig into the snow and prevent such turning.
The width of the tracks found on available snow cats is relatively narrow for a variety of reasons. The primary reason is that such track assemblies ride on a single row of wheels or casters which only provide a limited lateral stability to the track, thus limiting the width of that track. Another reason is that the load of the vehicle is carried at the center of the track, and if the grouser portion of the track spans a crevice or gap in the snow, the stress on the grousers will cause them to bend. Most available snow cats use grousers which have a relatively large cross section in order to achieve the desired bending strength. However, such a large cross section is undesirable when the snow cat is used to groom ski slopes because the grousers will then throw up large chunks of snow rather than create a smooth cured slope. Also a large narrow grouser does not dig into packed snow or ice as efficiently as a small wide grouser.
Many snow cats utilize a track assembly which has a plurality of tandem rollers wherein the lower surface of the roller rides on the track and the upper surface of the roller provides the return path for the track. One disadvantage of such a construction is that one of the rollers must be used as the drive roller, and the differential and drive axle must be relatively low to correspond with the center of the drive roller. Hence, the drive axle and differential often come into contact with the snow. When the rollers are made larger to raise the position of the drive axle and differential farther off the ground, the portion of track which circumscribes the fore and aft rollers is relatively large, and minimizes the proportion of track which is in contact with the snow. Hence, a relatively large amount of track must be used in order to have a sufficient length of track in contact with the snow.